Silanediol versus chlorosilanol: hydrolyses and hydrogen-bonding catalyses with fenchole-based silanes

• Falco Fox,
• Jörg M. Neudörfl and
• Bernd Goldfuss

Beilstein J. Org. Chem. 2019, 15, 167–186, doi:10.3762/bjoc.15.17

• kinetic study for the hydrolysis of dichlorosilane 7 shows a 263 times slower reaction compared to reference bis-(2,4,6-tri-tert-butylphenoxy)dichlorosilane (14), known for its low hydrolytic reactivity. Computational analyses explain the slow hydrolyses of BIFOXSiCl2 (7) to BIFOXSiCl(OH) (8, Ea = 32.6

• for side attack mechanism (Table 3, entry 10)) than the first. In accordance with the kinetic study, dichlorosilane 13 hydrolysed faster than BIFOXSiCl2 (7, Scheme 4). In addition, the hydrolysis of glycol-based dichlorosilane (Table 3, entries 11 and 12) and tetrachlorosilane (Table 3, entries 13 to

• ). Hydrogen-bond-catalyzed addition of silyl ketene acetals 11a–d with chromone 20 to product 22 with chlorosilanol 8 and silanediol 9 in toluenea (Scheme 8). Supporting Information Supporting Information File 42: Copies of all NMR spectra, HPLC graphs, GC graphs of the kinetic study. Acknowledgements We

Adhesion, forces and the stability of interfaces

• Robin Guttmann,
• Johannes Hoja,
• Christoph Lechner,
• Reinhard J. Maurer and
• Alexander F. Sax

Beilstein J. Org. Chem. 2019, 15, 106–129, doi:10.3762/bjoc.15.12

Asymmetric synthesis of a high added value chiral amine using immobilized ω-transaminases

• Antonella Petri,
• Valeria Colonna and
• Oreste Piccolo

Beilstein J. Org. Chem. 2019, 15, 60–66, doi:10.3762/bjoc.15.6

• are easily regenerated in situ without the need for another enzyme. In principle, enantiomerically pure chiral amines can be prepared following two approaches: through kinetic resolution starting from racemic amines or by asymmetric synthesis starting from suitable substrates, e.g., the corresponding

• carbonyl compounds. In a kinetic resolution, a maximum yield of 50% of the product can be obtained. Moreover, high quantities of the co-product might complicate the product separation and the recovery of the chiral amine. Thus, the asymmetric synthesis is generally preferable because a theoretically 100

• commercial free form or isolated from bacterial sources, both in kinetic resolution starting from the corresponding racemic amine and in asymmetric synthesis starting from the corresponding ketone. The first method, although it proceeds with high enantioselectivity, is a kinetic resolution and as a

Selective ring-opening metathesis polymerization (ROMP) of cyclobutenes. Unsymmetrical ladderphane containing polycyclobutene and polynorbornene strands

• Yuan-Zhen Ke,
• Shou-Ling Huang,
• Guoqiao Lai and
• Tien-Yau Luh

Beilstein J. Org. Chem. 2019, 15, 44–51, doi:10.3762/bjoc.15.4

• , 128.5, 131.8, 132.0, 150.5, 168.1, 171.6. General procedure for kinetic measurements Monomer 4 or 5 (0.03 mmol) was dissolved in DCM-d2 or THF-d8 (0.5 mL) and was syringed into an NMR tube inside a glove-box under nitrogen atmosphere. The NMR tube was then covered with a standard tube cap and placed in

• . Cyclopolymerization of 15 with a flexible linker. Methanolysis of unsymmetrical ladderphane 8. Supporting Information Supporting Information File 10: 1H and 13C NMR spectra of both monomers and polymers, as well as GPC and kinetic investigation results. Acknowledgement We thank the Ministry of Science and

Mechanistic studies of an L-proline-catalyzed pyridazine formation involving a Diels–Alder reaction with inverse electron demand

• Anne Schnell,
• J. Alexander Willms,
• S. Nozinovic and
• Marianne Engeser

Beilstein J. Org. Chem. 2019, 15, 30–43, doi:10.3762/bjoc.15.3

• contrast to the other two intermediates might indicate that the [4 + 2] cycloaddition between enamine intermediate I3 and tetrazine substrate 2 in R3 does not proceed as easily as for the untagged reaction R1 discussed above. This difference in the kinetic behavior might be due to the higher steric

• mL) from Hamilton and syringe pumps (single and double) from Cole Parmer were used. All kinetic 1H NMR experiments were conducted with a Bruker Avance III HD Ascend 700 MHz spectrometer equipped with a 5 mm QCI H-P/C/N cryoprobe with Z-gradient coils. The sample was shimmed before the first

New standards for collecting and fitting steady state kinetic data

• Kenneth A. Johnson

Beilstein J. Org. Chem. 2019, 15, 16–29, doi:10.3762/bjoc.15.2

• important parameter as it is used to quantify enzyme specificity, efficiency and proficiency [4][5]. In fact, kcat and kcat/Km should be considered as the two primary steady state kinetic parameters, rather than kcat and Km. A half century ago Cleland stressed that the two fundamental steady state kinetic

• defines 1/kcat and the slope defines 1/kcat/Km. In Cleland’s analysis, the two primary steady state kinetic parameters were kcat and kcat/Km because they were the parameters derived in fitting data displayed on a double reciprocal plot. Today, the emphasis is on interpreting the steady state kinetic

• parameters in terms of enzyme structure and individual steps in the reaction pathway. This leads to a new justification for choosing kcat/Km rather than Km as a primary kinetic parameter. Of the three steady state parameters (kcat, Km, and kcat/Km) kcat/Km is the most important as it quantifies enzyme

Ruthenium-based olefin metathesis catalysts with monodentate unsymmetrical NHC ligands

• Veronica Paradiso,
• Chiara Costabile and
• Fabia Grisi

Beilstein J. Org. Chem. 2018, 14, 3122–3149, doi:10.3762/bjoc.14.292

• kinetic behavior in the RCM of diethyl diallylmalonate (7, Scheme 1; reaction temperature 40 °C), where 117 displayed a higher activity than catalyst 116. Furthermore, they showed surprising selectivity (E/Z ratio around 3) in the CM of allylbenzene (13) and cis-1,4-diacetoxy-2-butene (Scheme 4; reaction

A simple and effective preparation of quercetin pentamethyl ether from quercetin

• Jin Tatsuzaki,
• Tomohiko Ohwada,
• Yuko Otani,
• Reiko Inagi and
• Tsutomu Ishikawa

Beilstein J. Org. Chem. 2018, 14, 3112–3121, doi:10.3762/bjoc.14.291

• unstable species among the anions 2A, and the negative charge of the anionic oxygen is small (−0.679). While the thermodynamic stability (instability) and kinetic reactivity in methylation reaction do not always coincide, these features are consistent with the experimental finding that the OH group at 5

Thermophilic phosphoribosyltransferases Thermus thermophilus HB27 in nucleotide synthesis

• Ilja V. Fateev,
• Ekaterina V. Sinitsina,
• Aiguzel U. Bikanasova,
• Maria A. Kostromina,
• Elena S. Tuzova,
• Larisa V. Esipova,
• Tatiana I. Muravyova,
• Alexei L. Kayushin,
• Irina D. Konstantinova and
• Roman S. Esipov

Beilstein J. Org. Chem. 2018, 14, 3098–3105, doi:10.3762/bjoc.14.289

• HB27 were expressed in E.coli strains and purified by chromatographic methods with yields of 10–13 mg per liter of culture. The activity dependence of TthAPRT and TthHPRT on different factors was investigated along with the substrate specificity towards different heterocyclic bases. The kinetic

• phosphoribosyltransferase Thermus thermophilus (TthHPRT), investigated its substrate specificity and optimal conditions for catalytic activity, and determined the kinetic parameters of the enzyme. A comparative study of the substrate specificity of TthAPRT and TthHPRT was performed to determine the usability of

• . After optimization of the reaction conditions, kinetic parameters for TthHPRT were determined (Table 2). Based on the Km values, the affinity of 5-phosphoribosyl-α-1-pyrophosphate for the active site is much lower than that of heterocyclic bases. The similar situation we observed for TthAPRT [1

Degenerative xanthate transfer to olefins under visible-light photocatalysis

• Atsushi Kaga,
• Xiangyang Wu,
• Joel Yi Jie Lim,
• Hirohito Hayashi,
• Yunpeng Lu,
• Edwin K. L. Yeow and
• Shunsuke Chiba

Beilstein J. Org. Chem. 2018, 14, 3047–3058, doi:10.3762/bjoc.14.283

•  2A. The band between 450 nm and 600 nm is attributed to the excited 3MLCT state of the photocatalyst [53][54][55]. The positive ΔOD feature in the UV region (<400 nm) is also ascribed to the excited 3MLCT state [55]. The transient kinetic profile probed at 480 nm decays mono-exponentially with a

• in Figure 2D. The kinetic profile at 480 nm is described using a mono-exponential decay function with a quenched lifetime of 1.27 μs. The ca. 37% decrease in the lifetime of the excited 3MLCT state of photocatalyst 8 observed in the PL lifetime decay measurement (Figure 1C) and ns-TA kinetic

• absorption spectra of photocatalyst 8 in degassed DMSO recorded at different delay times (excitation wavelength = 355 nm). (B) ns-TA kinetic profile probed at 480 nm for photocatalyst 8 in the absence and presence of xanthate 1a. (C) and (D) ns-Transient absorption spectra of xanthate 1a and 8 in the

A tutorial review of stereoretentive olefin metathesis based on ruthenium dithiolate catalysts

• Daniel S. Müller,
• Olivier Baslé and
• Marc Mauduit

Beilstein J. Org. Chem. 2018, 14, 2999–3010, doi:10.3762/bjoc.14.279

• . Therefore, trisubstituted alkenes work best with the same catalysts used for E-alkenes (e.g., Ru-7, Ru-8 and Ru-9). 3 Kinetic studies Grubbs studied the kinetic behavior of several Ru-dithiolate catalysts [6][14][15]. In a typical study the disappearance of the benzylidene proton of the ruthenium complex

Olefin metathesis catalysts embedded in β-barrel proteins: creating artificial metalloproteins for olefin metathesis

• Daniel F. Sauer,
• Johannes Schiffels,
• Takashi Hayashi,
• Ulrich Schwaneberg and
• Jun Okuda

Beilstein J. Org. Chem. 2018, 14, 2861–2871, doi:10.3762/bjoc.14.265

• of the catalyst inside the cells and the transport within organisms without triggering or activating a response of the corresponding target [15]. Additionally, the (kinetic) stability of the catalysts in aqueous solutions needs to be improved for this purpose. For application in organic synthesis in

Synthesis of pyrrolidine-based hamamelitannin analogues as quorum sensing inhibitors in Staphylococcus aureus

• Jakob Bouton,
• Kristof Van Hecke,
• Reuven Rasooly and
• Serge Van Calenbergh

Beilstein J. Org. Chem. 2018, 14, 2822–2828, doi:10.3762/bjoc.14.260

• previous attempts to synthesize 9 failed due to side reactions caused by the strongly electron-withdrawing properties of the nosyl group. The successful synthesis starts with a Pd-catalyzed dynamic kinetic asymmetric transformation of racemic butadiene monoepoxide to 12, employing phthalimide as

Cobalt- and rhodium-catalyzed carboxylation using carbon dioxide as the C1 source

• Tetsuaki Fujihara and
• Yasushi Tsuji

Beilstein J. Org. Chem. 2018, 14, 2435–2460, doi:10.3762/bjoc.14.221

• kinetic stability of CO2 sometimes limits its utility. Classically, harsh reaction conditions such as high temperature and high pressure of CO2 were required. To overcome these problems, the use of transition-metal catalysts has been considered as a fundamental and reliable method. In the last decade

Some mechanistic aspects regarding the Suzuki–Miyaura reaction between selected ortho-substituted phenylboronic acids and 3,4,5-tribromo-2,6-dimethylpyridine

• Piotr Pomarański,
• Piotr Roszkowski,
• Jan K. Maurin,
• Armand Budzianowski and
• Zbigniew Czarnocki

Beilstein J. Org. Chem. 2018, 14, 2384–2393, doi:10.3762/bjoc.14.214

• product of coupling in the group of disubstituted compounds is (syn)-7 (Table 1, entries 1–13) although it is thermodynamically unstable (kinetic product). Apparently, the selectivity in the case of the use of ortho-methoxyphenylboronic acid is also governed by an additional metal O-chelation effect in

• ). Considering further applications of atropisomeric arylated pyridines in the design of new materials like molecular switches [4], it would be desirable to estimate their thermal stability. We therefore performed kinetic experiments in order to establish the value of the barrier to rotation in the

• stereoisomers of 3,4,5-tris(2-methoxyphenyl)-2,6-dimethylpyridines determined by X-ray analysis [38]. Graphical representation of kinetic, time-dependent 1H NMR analysis of (syn)-7 (100 °C). Graphical representation of kinetic, time-dependent 1H NMR analysis of (syn)-10 (120 °C). HT-NMR (300 MHz, DMSO-d6

A challenging redox neutral Cp*Co(III)-catalysed alkylation of acetanilides with 3-buten-2-one: synthesis and key insights into the mechanism through DFT calculations

• Andrew Kenny,
• Alba Pisarello,
• Arron Bird,
• Paula G. Chirila,
• Alex Hamilton and
• Christopher J. Whiteoak

Beilstein J. Org. Chem. 2018, 14, 2366–2374, doi:10.3762/bjoc.14.212

• energy difference between the C–H activation and C–C bond formation steps makes identification of the rate limiting step difficult by DFT calculations alone, however, parallel kinetic isotope effect (KIE) experiments do suggest that the C–H activation step is not rate limiting (KIE = 1.3), which is not

Non-metal-templated approaches to bis(borane) derivatives of macrocyclic dibridgehead diphosphines via alkene metathesis

• Tobias Fiedler,
• Michał Barbasiewicz,
• Michael Stollenz and
• John A. Gladysz

Beilstein J. Org. Chem. 2018, 14, 2354–2365, doi:10.3762/bjoc.14.211

• the P(CH2)6CH=CH(CH2)6P tether. Importantly, all of these steps are presumed to be largely under kinetic control, consistent with experience with the types of metatheses in Scheme 1 [1][2][3][4][5][6][7][8][9][10][11][12][13][34]. Although the second route intuitively seems more favorable, after the

• result (as drawn in Scheme 7, the out,out isomer would be the kinetic product). When the first metathesis does not join the syn positions, as in VIII (front to rear), one phosphorus–boron bond must subsequently be rotated by 180° to create a syn orientation for the second metathesis. Of course, if the

Bioinspired cobalt cubanes with tunable redox potentials for photocatalytic water oxidation and CO₂ reduction

• Zhishan Luo,
• Yidong Hou,
• Jinshui Zhang,
• Sibo Wang and
• Xinchen Wang

Beilstein J. Org. Chem. 2018, 14, 2331–2339, doi:10.3762/bjoc.14.208

• photosynthetic systems [8][9][10][11][12][13]. However, such target reactions are typical thermodynamically uphill reactions with large overpotentials, leading to low conversion efficiency. Therefore, the search for suitable cocatalysts to reduce the multielectron involved kinetic barriers for water oxidation

• , because of their well-controlled functions and tunable nature [20][21]. Their topologies and electron structures can be precisely engineered by ligand design, using the full arsenal of organic chemistry [22][23]. These unique structures benefit not only tailoring their redox and kinetic properties for

The enzymes of microbial nicotine metabolism

• Paul F. Fitzpatrick

Beilstein J. Org. Chem. 2018, 14, 2295–2307, doi:10.3762/bjoc.14.204

• are both reported to have the ability to catalyze this reaction [48]. NicA1 was also reported to catalyze the subsequent oxidation of pseudooxynicotine to 3-succinylpyridine and methylamine, but no kinetic parameters for the two reactions were reported [51]. However, deletion of nicA2 but not of nicA1

• -dihydroxypyridine [57]. The sequence of the protein is not similar to that of any proteins with known functions. Purified recombinant HspA was reported to require NADH to catalyze the cleavage of 6-hydroxy-3-succinoylpyridine, but detailed kinetic analyses were not done. However, levels of HspA do not increase when

• E. coli and the purified protein shown to be an LHNO similar to the enzyme from A. nicotinovorans in its kinetic properties [18][75]. The genes responsible for the other enzymes were tentatively identified by comparison with the sequences of the enzymes from Ochrobactrum sp. SJY1 and A. tumefaciens

Determining the predominant tautomeric structure of iodine-based group-transfer reagents by ¹⁷O NMR spectroscopy

• Nico Santschi,
• Cody Ross Pitts,
• Benson J. Jelier and
• René Verel

Beilstein J. Org. Chem. 2018, 14, 2289–2294, doi:10.3762/bjoc.14.203

• over 50 kcal/mol, a high kinetic barrier suppresses the [a → b] isomerization (Figure 1) [5][6]. With SCF3 reagent 5a/5b, structure determination was notably challenging and solely provides a solid-state structural perspective. Thus, we wondered whether a correct structural assignment of reagent 5a/b

Hydroarylations by cobalt-catalyzed C–H activation

• Rajagopal Santhoshkumar and
• Chien-Hong Cheng

Beilstein J. Org. Chem. 2018, 14, 2266–2288, doi:10.3762/bjoc.14.202

• found intermolecular kinetic isotope effect (KIE) of kH/kD = 2.1 and H/D crossover studies strongly suggest that the reaction proceeds through an oxidative addition of a C–H bond to low-valent cobalt followed by alkyne insertion and reductive elimination. Furthermore, the new C–C bond formation occurred

Synthesis and post-functionalization of alternate-linked-meta-para-[2ⁿ.1ⁿ]thiacyclophanes

• Wout De Leger,
• Koen Adriaensen,
• Koen Robeyns,
• Luc Van Meervelt,
• Joice Thomas,
• Björn Meijers,
• Mario Smet and
• Wim Dehaen

Beilstein J. Org. Chem. 2018, 14, 2190–2197, doi:10.3762/bjoc.14.192

• the [2 + 2] adduct 6 is the more thermodynamically favoured product and the [3 + 3] adduct 7 is the kinetic product. When the reaction was carried out at higher temperatures, an increase in the formation of open chain oligomers was observed (Supporting Information File 1, Table S1, entries 13 and 14

Calix[6]arene-based atropoisomeric pseudo[2]rotaxanes

• Carmine Gaeta,
• Carmen Talotta and
• Placido Neri

Beilstein J. Org. Chem. 2018, 14, 2112–2124, doi:10.3762/bjoc.14.186

• axle. In all the examined cases, the 1,2,3-alternate and cone atropoisomers are, respectively, the kinetic and the thermodynamic ones. Keywords: atropoisomers; calixarene; conformation; pseudorotaxane; social isomerism; Introduction Mechanomolecules [1][2][3][4], such as rotaxanes and catenanes show

• were observed as the kinetic and thermodynamic adduct, respectively, with an interconversion time of 12 h at 353 K. A further example regards the threading of the narrower penta-O-methyl-p-tert-butylcalix[5]arene 7 with pentylbenzylammonium axle 8+ [35]. Two atropoisomeric pseudorotaxanes were formed

• , namely 8+7cone and 8+7paco (Figure 9), in which the calix[5]-wheel adopted a cone and a partial-cone conformation, respectively [35]. Also in this case, the atropoisomer with an “inverted” calixarene wheel 8+7paco is the kinetic product, while the other with a calix-cone conformation 8+7cone is the

Revisiting ring-degenerate rearrangements of 1-substituted-4-imino-1,2,3-triazoles

• James T. Fletcher,
• Matthew D. Hanson,
• Joseph A. Christensen and
• Eric M. Villa

Beilstein J. Org. Chem. 2018, 14, 2098–2105, doi:10.3762/bjoc.14.184

• four imine products via a dynamic equilibrium of condensation, rearrangement and hydrolysis steps. Kinetic studies utilizing 1-(4-nitrophenyl)-1H-1,2,3-triazole-4-carbaldehyde with varying amines showed rearrangement rates sensitive to both steric and electronic factors. Such measurements were

• would inform the design of stable 4-imino-1,2,3-triazole target compounds, while a better understanding of parameters promoting this rearrangement might lead to improved methodology for the preparation of 1-subsituted-4-formyl-1,2,3-triazole target compounds. An expanded thermodynamic and kinetic

• useful synthon for formyltriazole preparations, it was used to prepare analogs 1c (59% isolated yield) and 1d (64% isolated yield) by the kinetic assay conditions (see Supporting Information File 1). Optimizing of reaction yields and exploring of the scope of amine reagents tolerated by this

D-Fructose-based spiro-fused PHOX ligands: synthesis and application in enantioselective allylic alkylation

• Michael R. Imrich,
• Jochen Kraft,
• Cäcilia Maichle-Mössmer and
• Thomas Ziegler

Beilstein J. Org. Chem. 2018, 14, 2082–2089, doi:10.3762/bjoc.14.182

• product in twist conformation. Due to the fact that the lower energy level of the chair conformation compared to the twist conformation is already present in the transition state the generation of the twist conformer is kinetically disfavored [39][40]. This kinetic phenomenon is sometimes called the Fürst